Description

Memory slices provide a space-efficient and multi-processing scalable
way to allocate equal-sized pieces of memory, just like the original
GMemChunks (from GLib <= 2.8), while avoiding their excessive
memory-waste, scalability and performance problems.

To achieve these goals, the slice allocator uses a sophisticated,
layered design that has been inspired by Bonwick's slab allocator
[6].
It uses posix_memalign() to optimize allocations of many equally-sized
chunks, and has per-thread free lists (the so-called magazine layer)
to quickly satisfy allocation requests of already known structure sizes.
This is accompanied by extra caching logic to keep freed memory around
for some time before returning it to the system. Memory that is unused
due to alignment constraints is used for cache colorization (random
distribution of chunk addresses) to improve CPU cache utilization. The
caching layer of the slice allocator adapts itself to high lock contention
to improve scalability.

The slice allocator can allocate blocks as small as two pointers, and
unlike malloc(), it does not reserve extra space per block. For large block
sizes, g_slice_new() and g_slice_alloc() will automatically delegate to the
system malloc() implementation. For newly written code it is recommended
to use the new g_slice API instead of g_malloc() and
friends, as long as objects are not resized during their lifetime and the
object size used at allocation time is still available when freeing.

GRealArray *array;/* Allocate one block, using the g_slice_new() macro. */
array =g_slice_new(GRealArray);/* We can now use array just like a normal pointer to a structure. */
array->data = NULL;
array->len =0;
array->alloc =0;
array->zero_terminated = (zero_terminated ? 1:0);
array->clear = (clear ? 1:0);
array->elt_size = elt_size;/* We can free the block, so it can be reused. */g_slice_free(GRealArray, array);

Details

g_slice_alloc ()

Allocates a block of memory from the slice allocator.
The block adress handed out can be expected to be aligned
to at least 1 * sizeof (void*),
though in general slices are 2 * sizeof (void*) bytes aligned,
if a malloc() fallback implementation is used instead,
the alignment may be reduced in a libc dependent fashion.
Note that the underlying slice allocation mechanism can
be changed with the G_SLICE=always-malloc
environment variable.

block_size :

the number of bytes to allocate

Returns :

a pointer to the allocated memory block

Since 2.10

g_slice_alloc0 ()

Allocates a block of memory via g_slice_alloc()
and initialize the returned memory to 0.
Note that the underlying slice allocation mechanism can
be changed with the G_SLICE=always-malloc
environment variable.

g_slice_free1 ()

Frees a block of memory. The memory must have been allocated via
g_slice_alloc() or g_slice_alloc0()
and the block_size has to match the size specified upon allocation.
Note that the exact release behaviour can be changed with the
G_DEBUG=gc-friendly environment variable,
also see G_SLICE for related debugging options.

block_size :

the size of the block

mem_block :

a pointer to the block to free

Since 2.10

g_slice_free_chain_with_offset ()

Frees a linked list of memory blocks of structure type type.
The memory blocks must be equal-sized, allocated via
g_slice_alloc() or g_slice_alloc0()
and linked together by a next pointer (similar to GSList). The offset
of the next field in each block is passed as third argument.
Note that the exact release behaviour can be changed with the
G_DEBUG=gc-friendly environment variable,
also see G_SLICE for related debugging options.

block_size :

the size of the blocks

mem_chain :

a pointer to the first block of the chain

next_offset :

the offset of the next field in the blocks

Since 2.10

g_slice_new()

#define g_slice_new(type)

A convenience macro to allocate a block of memory from the slice allocator.
It calls g_slice_alloc() with sizeof (type) and casts
the returned pointer to a pointer of the given type, avoiding a type cast
in the source code.
Note that the underlying slice allocation mechanism can
be changed with the G_SLICE=always-malloc
environment variable.

type :

the type to allocate, typically a structure name

Returns :

a pointer to the allocated block, cast to a pointer to type.

Since 2.10

g_slice_new0()

#define g_slice_new0(type)

A convenience macro to allocate a block of memory from the slice allocator
and set the memory to 0. It calls g_slice_alloc0() with
sizeof (type) and casts the returned pointer to a pointer
of the given type, avoiding a type cast in the source code.
Note that the underlying slice allocation mechanism can
be changed with the G_SLICE=always-malloc
environment variable.

type :

the type to allocate, typically a structure name

Returns :

a pointer to the allocated block, cast to a pointer to type.

Since 2.10

g_slice_dup()

#define g_slice_dup(type, mem)

A convenience macro to duplicate a block of memory using the slice allocator.
It calls g_slice_copy() with sizeof (type) and casts
the returned pointer to a pointer of the given type, avoiding a type cast
in the source code.
Note that the underlying slice allocation mechanism can
be changed with the G_SLICE=always-malloc
environment variable.

type :

the type to duplicate, typically a structure name

mem :

the memory to copy into the allocated block

Returns :

a pointer to the allocated block, cast to a pointer to type.

Since 2.14

g_slice_free()

#define g_slice_free(type, mem)

A convenience macro to free a block of memory that has been allocated
from the slice allocator. It calls g_slice_free1() using
sizeof (type) as the block size.
Note that the exact release behaviour can be changed with the
G_DEBUG=gc-friendly environment variable,
also see G_SLICE for related debugging options.

type :

the type of the block to free, typically a structure name

mem :

a pointer to the block to free

Since 2.10

g_slice_free_chain()

#define g_slice_free_chain(type, mem_chain, next)

Frees a linked list of memory blocks of structure type type.
The memory blocks must be equal-sized, allocated via
g_slice_alloc() or g_slice_alloc0() and linked together by a
next pointer (similar to GSList). The name of the
next field in type is passed as third argument.
Note that the exact release behaviour can be changed with the
G_DEBUG=gc-friendly environment variable,
also see G_SLICE for related debugging options.